Magnetic read-write heads typically include two magnetic shields that are important for the reader part—the shield S1 below the read sensor, also called the bottom shield, and shield S2 immediately above the sensor, also called the top shield. Current typical thick film shield designs have several problems, including magnetic stability problems, increased spacing between reader and writer, and manufacturing and other issues. Changes in shield magnetic domain states can cause sensor signal changes; these are the so-called shield magnetic stability problems which may arise from applied external fields, media fields, internal write head related or thermal stresses, or even from statistical equilibrium state changes. A new shield design is disclosed that overcomes these problems.
These, and other limitations of the prior art can be seen in the references that we review immediately below:
U.S. Pat. No. 7,180,712 by Min Li et al. describes a laminated shield using Ru, but no AFM; it applies to MR heads, not TMR/CPP. Without the AFM layers, the shield may rotate or switch as a whole, as there is no single preferred orientation. The present invention applies to TMR/CPP and GMR/CPP devices. Min's patent also has undercoat limitations, which are not relevant for the present invention.
U.S. Pat. No. 6,801,409 by Richard Michel et al. also applies to MR heads. It describes a non-laminated shield that employs an AFM to pin the shield. It is thus a single ferromagnetic(FM) layer, which is different from the present invention. In Michel's patent, the shield domain pattern is, ideally, stabilized and locked in by setting the AFM during an anneal; but as the shield is a monolayer it will have a large net moment, and is thus much harder to stabilize. There is no discussion of film thicknesses.
U.S. Pat. No. 7,236,333 by Macken and Daclen applies to MR heads also. They employ an AFM pinned bilayer, but with ferromagnetic bilayer decoupled through a non-magnetic thick spacer layer. U.S. Patent Application 2007/0195467 (Gill) shows a second shield layer comprising a FM layer, an AFM layer, and a non-magnetic layer.
U.S. Patent Application 2007/0139826 (Carey et al) discloses a shield with anisotropy achieved by use of textured surfaces. U.S. Pat. No. 6,496,335 (Gill) shows FM layers separated by spacer layers such as Ru as a shield, but does not include AFM layers as part of the system. Also, it claims a net moment for the FM layers, and applies to GMR/CPP heads. In U.S. Pat. No. 6,456,467, Mao et al. disclose “Laminated shields with antiparallel magnetizations”. This work does not include an AFM pinning layer.